1. Field of the Invention
The present invention relates to an ink-jet printing system. More particularly, the present invention relates to a printing system comprising an ink receiving sheet adapted to be used with a concentrated ink, especially for obtaining medical images showing high optical density by using an ink-jet printer.
2. Background of the Art
In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the recording medium. The ink droplets, toner, or recording liquid generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An ink jet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-recording layer. The recording elements may include either those intended for reflection viewing, which have an opaque support, or those intended for viewing by transmitted light, which have a transparent support.
Medical images, such as radiographic images, are typically viewed on a blue transparent support and require a high optical density, i.e., usually higher than 3.00. Medical images of such a high optical density are typically obtained by means of silver technology, in which the image is formed by exposing a light-sensitive silver salt and the subsequent formation of black silver by development (reduction) of the light-sensitized silver salt.
The progress and development of the ink-jet technology and the higher costs associated with the silver technology have increased the desirability of and the demand for obtaining medical images with the ink-jet technology.
However, ink jet technology involves a problem unique to the technology. When high-density printing is conducted on a transparent recording medium, relatively high maximum optical densities in image are harder to achieve as compared with the relatively high optical density of images obtained with the silver salt method. This is a result of the high transparency of the coloring material.
U.S. Pat. Nos. 6,342,096, 6,341,855 and 6,059,404 attempt to solve this problem of low maximum optical densities by providing an ink-jet recording method using a mix of different inks printed on a receiving sheet that is adapted to receive such different inks. This solution has proved expensive and has not led to good results.
U.S. Pat. Nos. 5,621,448 and 5,621,449 attempt to solve this ink-jet density problem with a combination of the silver and ink-jet technologies. U.S. Pat. No. 5,621,448 discloses a recording method comprising the consecutive steps of: (1) image-wise projecting droplets of liquid, called ink, containing halide ions, onto a receiving material containing at least one substantially light-insensitive silver salt. The ink and/or receiving material contains at least one reducing agent for the silver salt, (2) uniformly photo-exposing the receiving material to form silver nuclei from silver halide obtained in step (1), and (3) heating the receiving material during and/or after the photo-exposure step. This forms a silver image in correspondence with the area wherein the ink has been deposited on the receiving material. U.S. Pat. No. 5,621,449 discloses an ink jet recording method comprising the steps of: (1) image-wise projecting liquid, called ink, in the form of droplets onto a receiving material. The receiving material contains a substance that, by chemically reacting with another substance contained in said droplets, is capable of forming a visually detectable product. The process is characterized in that according to a first mode, the receiving material contains at least one substantially light-insensitive organic silver salt and the ink contains a reducing agent for the silver salt, and according to a second mode the receiving material contains the reducing agent and the ink contains the silver salt, and optionally (2) heating the receiving material during and/or after the deposition of the ink on the receiving material to start or enhance reduction of the silver salt(s) forming thereby image-wise a deposit of silver metal in the receiving material. This solution to obtaining higher density ink-jet images is still expensive and requires special apparatus and several steps in order to get the desired images.
U.S. Pat. No. 4,503,111 discloses an ink-jet receiving sheet comprising a support coated with an ink receiving layer. The support, consisting of a transparent base sheet, such as cellulose acetate or polyethylene terephthalate, is coated with a mixture of polyvinylpyrrolidone and a compatible matrix-forming polymer, such as gelatin or polyvinyl alcohol. The sheet is disclosed to be used in ink jet printers and in pen-type graphics recorders to record large color-filled areas with high color density and excellent resolution.
An ink jet printing system comprises an ink receiving sheet and an ink-jet printer. The ink receiving sheet comprises a support, at least one receiving layer and a top coat layer. The ink-jet printer comprises an ink-jet cartridge comprising an ink. The receiving layer comprises a hydrophilic binder and a vinyl polymeric compound and has a total coverage weight of at least 12 g/m2, and the top coat layer is free of vinyl polymeric compounds and comprises a hydrophilic binder and a corn starch matting agent. The ink comprises a dye selected from the group consisting of azo and disazo dye at a concentration higher than 4% by weight, in order to achieve an optical density higher than 3.00.